This invention relates to storing digital data on mechanically-driven storage media, such as magnetic disks.
In a typical magnetic disk drive, several hard magnetic disks are mounted on a single rotating spindle. The storage space on each disk surface is organized in concentric tracks. The corresponding tracks on all of the disk surfaces form an imaginary cylinder. Each disk surface is served by a read/write head. All of the read/write heads can be moved together to any selected cylinder and can then store or retrieve data on the tracks that make up that cylinder.
Normally the magnetic disk drive is connected by a serial bus to a disk controller that, among other things, directs the read/write heads to move to the proper track, buffers data that is about to be stored on or has just been retrieved from the disk, assures that the data is stored or retrieved at the proper address, and performs serial error correction and detection on the data. Typically the disk controller serves a parallel input/output bus connected to a computer whose input/output port is, for example, 32 bits wide. Thirty-two bit words delivered over the bus are passed via the disk controller and serially loaded onto or retrieved from the disk drive. The throughput rate of the serial bus between the disk controller and the disk drive is roughly matched to the throughput rate of the parallel I/O bus between the computer and the disk controller.
In order to expand the total available storage space, multiple disk driver can be linked to a single controller in a daisy chain or star configuration.